Liquid crystal display (LCD) is commonly used as a display device because of its capability of displaying images with good quality while using little power. An LCD device includes an LCD panel formed with liquid crystal cells and pixels associating with the liquid crystal cells. These pixels are substantially arranged in the form of a matrix having a number of pixel rows and a number of pixel columns. Gate signals and data signals are respectively applied to the pixel rows and the pixel columns to align states of the liquid crystals to control light transmission through the pixels for the entire LCD panel so as to display frames through the input of image data of respective pixels. Since the pixels can only display the grey level from brightness to darkness, other means are needed for the display of colors.
Referring to FIG. 7, a conventional LCD 700 displays colors through color filters that display the three primary color components of a pixel at the same time. Each pixel of the color filter LCD panel 710 includes three displaying units respectively corresponding to a red filter 722, a green filter 724 and a blue filter 726. The red light 732, green light 734 and blue light 736 displayed respectively via the filters 722, 724 and 726 are combined and the colors of the pixel are perceived by the viewer. However, the use of color filters for color display in LCD panels not only increases the manufacturing cost of LCDs, but also reduces the light transmission therethrough.
FIG. 8 shows a conventional color-sequential LCD 800 that displays colors by sequentially displaying the components of the three primary colors 832, 834 and 836 of a pixel. The color-sequential LCD 800 includes a backlight unit capable of emitting, for example, red light 822, green light 824 and blue light 826 respectively from three light sources for each pixel 850. During a frame time, the pixel sequentially displays three sub-frames 832, 834, and 836 of data and the red light, green light and blue light sources are sequentially turned on. Through the persistence of vision, a viewer is able to recognize the color of a pixel.
Compared with the color filter LCDs, a color-sequential LCD displays colors without using color filters, and therefore is advantageous in cost saving and light transmission. Additionally, the color-sequential LCD displays the color of a pixel using only one pixel, thereby increasing the resolution of the LCD by three times. However, for such a color-sequential LCD, image data is input to a pixel sequentially in three times in order to completely input the image data to the pixel, thereby requiring the liquid crystals with much shorter response time. For example, in a color filter LCD, if an image is refreshed at 60 Hz, it makes the time period of one frame about 16.7 ms. Since an image for one color must be displayed within a ⅓ period of 16.7 ms for one frame, the time period used for display a sub-frame of an image is about 5.56 ms in a color-sequential LCD. Therefore, liquid crystals in the color-sequential LCD itself are required to have a response time shorter than 5.56 ms.
Referring to FIG. 9A, an LCD device 900 having an LCD panel 910 having gates A, B and C is shown. When gate signals 922, 924 and 926 generated from a gate driver 920 are sequentially applied to gates A, B and C, respectively, gate C is activated at very last, and therefore, the liquid crystals associated with gate C are driven by data signals 952 and 954 generated from a data driver 950 at very last as well. Ideally, a corresponding backlight is turned on after the liquid crystals associated with all gates including gate C are aligned in their predetermined state in accordance with the data signals 952 and 954. In practice, due to the response time not short enough, the liquid crystals associated with gate C may not be fully aligned when the backlight is turned on, thereby causing non-uniform brightness from the top to the bottom of the LCD panel. As shown in FIG. 9B, for the gate A, the response of the corresponding liquid crystals completes at time t1, while the corresponding liquid crystals of the gate C fully respond at time t3. The backlight, such as light emitting diodes (LEDs), is turned on and off at times t2 and t4. The luminance through the gates A and C in the first scan period are respectively corresponding to areas 991 and 993, which are substantially different.
FIGS. 10A and 10B show the gamma curves for a conventional display panel and a conventional color-sequential LCD panel, respectively. As shown in FIG. 10A, the conventional display panel has a single gamma curve 1010 over the entire panel such that the light transmittance (brightness) through the entire display panel is uniform for a given grey level. However, for a color-sequential LCD panel, different areas of the LCD panel have different gammas. As shown in FIG. 10B, areas A, B and C have gamma curves 1052, 1054 and 1056, respectively. For a given grey level, for example, L0, the light transmittance through the areas A, B and C are Ta, Tb and Tc, respectively, where Ta>Tb>Tc. Therefore, the brightness is non-uniform over the LCD panel.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.